I've spent the last month (almost) playing with Google Wave and I love it. There's only a few problems that, more than likely, will be addressed before it goes "live". First, when you only have a handful of people in your contacts list, and none of them are online very often - if at all, there's no conversation. So, you send someone a message and that's it. Two weeks later, when they think about it, you get a response. It's not mainstream enough for them to go there often. It's kind of like the early days of email. You only have a handful of people that actually have access to email. And those that do never check it.
Will Wave be successful? Absolutely. Will it take time? Unfortunately yes. Are you willing to wait?